Electrodeposition of strippable metal coatings and compositions and artiticles useful therefor



United States Patent 01 fice 3,523,873 Patented Aug. 11, 1970 3,523,873ELECTRODEPOSITION F STRIPPABLE METAL COATINGS AND COMPOSITIONS AND ARTI-TICLES USEFUL THEREFOR Eugene Mitchell Elkin, Montreal, Quebec, Canada,as-

signor to Canadian Copper Refiners Limited, Toronto, Ontario, Canada, acorporation of Canada No Drawing. Filed Dec. 14, 1965, Ser. No. 513,854Int. Cl. C23b 7/ 00, 7/02 US. Cl. 204-3 10 Claims ABSTRACT OF THEDISCLOSURE It has been found that a dressing or parting agentcomposition comprising an aqueous emulsion containing minor amounts byway of a polar, saturated, substantially waterinsoluble aliphaticorganic compound or a sulfur-containing material is useful and yieldsimproved results when employed in an operation for the preparation ofmetal cathode starting sheets, such as copper cathode starting sheets.

This invention relates to the electrodeposition of metals. Moreparticularly, this invention relates to the electrodeposition of metalsonto a substrate, such as a metal or electrically conductive substrate,under conditions such that the electrodepositioned metal is readilyseparable or stripable from the substrate.

In accordance with one embodiment this invention is directed to a methodof making a metal cathode starting sheet, such as a continuous,coherent, essentially holefree copper cathode starting sheet, useful inthe electrorefining of metals. In accordance with another embodimentthis invention is directed to an electrically conductive substratecoated with a parting agent, which permits the ready separation ofelectrodeposited metal from the coated substrate. In accordance with yetanother embodiment, this invention is directed to a parting agentcomposition useful in the manufacture of metal cathode starting sheets,such as copper cathode starting sheets, employed in the electrorefiningof metals. In accordance with still another embodiment, this inventionis directed to a parting agent composition useful in electroformingoperations.

Although emphasis is placed in the disclosure of this invention on theapplicability of the invention to the electrorefining of copper and tothe manufacture of copper cathode starting sheets, the practices and thevarious embodiments of this invention also appear to be applicable inthe electrorefining of other metals including nickel and the like,particularly in electrorefining operations wherein substantially puremetal is electrodeposited upon a smooth metal substrate and theresulting electrodeposited metal stripped or otherwise removed from themetal substrate in the form of a thin, smooth, coherent, substantiallyholefree sheet.

In the preparation of copper cathode starting sheets useful in theelectrorefining of copper, copper is electrodeposited upon a smoothmetal sheet or blank, such as a smooth plate of rolled copper, which hasbeen coated with a parting agent. The essential functions of the partingagent are to provide a suitable surface for the electrodeposition ofcopper, to prevent adherence of the electrodeposited copper to thecopper plate and to facilitate the removal or stripping of theelectrodeposited copper from the copper plate in the form of acontinuous, coherent, subsubstantially hole-free sheet.

It has been a practice heretofore to coat the surface of the blank usedin the electrodeposition of metal with a film of a petroleum derivedparting agent or dressing usually comprising a lubricating oil,transformer oil, diesel oil or fuel oil or mixtures thereof, includinglubricating greases and gasoline. Such dressings or parting agents areusually applied by hand swabs or rollers or by dipping in a tankcontaining such dressings and by other means.

It has also been suggested to employ as a dressing 9. waterabase solubleoil emulsion, see Cadwell-U.S. 3,046,- 203 issued July 24, 1962. Also,it is not uncommon to include in parting agent compositions variousadditives, such as anti-oxidants, anti-foam agents, germicides, wettingagents and the like. However, it has been experienced in actualcommercial operations for the preparation of copper cathode startingsheets that when dressings or parting agents containing apetroleum-derived material or a petroleum composition are employed,non-uniform results are often obtained. It appears thatpetroleum-derived or petroleum products vary, depending upon themanufacturer, the source of the crude petroleum and the type and/ orseverity of refining to which the petroleum product has been subjected.These variations in the origin and the processing of such petroleumproducts influence the performance of such petroleum products whenemployed as a dressing or parting agent in the manufacture of startingsheets, such as copper cathode starting sheets.

For example, petroleum products when employed as dressings in thepreparation of copper cathode starting sheets sometimes appear to causeholes in the sheets, presumably caused by excess amounts of petroleumproduct as well as by unknown causes. Also, roughness of theelectrodeposited copper sheet accompanied by sharp protuberances isoften observed. Further, a rash of smooth, rounded-01f pimplesirregularly covering the surface of the electrodeposited copper,difficulty in initiating the parting or separation of theelectrodeposited copper from the copper blank, difficulty in strippingor parting the electrodeposited copper from the copper blank, difficultyin separating and pullling off the electrodeposited copper from aroundthe side edges of the copper blank and formation of finely dividedelectrodeposited dust on the surface of the copper blank have also beenobserved and experienced when parting agents containing petroleum derived materials or compositions are employed. Ihe aforementioned dusttends to become firmly attached to the copper blank and to roughen itssurface with eventual detrimental affect upon the stripping operation.

Because of these difficulties observed when petroleumcontainingdressings are employed in the production of copper cathode startingsheets, it has been experienced that about 5-l0% of the copper cathodestarting sheets are defective. It has also been experienced that uponthose occasions when the petroleum supplier and/or manufacturer changessources or refining techniques the percentage of defective coppercathode starting sheets may increase up to 25% and even higher of thetotal number of sheets produced.

Accordingly, it is an object of this invention to provide a dressing orparting agent of controlled composition.

It is another object of this invention to provide an improvedelectroforming operation involving the production of strippableelectroformed metal products.

It is yet another object of this invention to provide an improvedprocess for the manufacture of cathode starting sheets useful in theelectrorefining of metals.

It is still another object of this invention to provide a coated,electrically conductive substrate useful in electroforming operationsand the like.

It is a specific object of this invention to provide an improved processfor the manufacture of copper cathode starting sheets.

Yet another specific object of this invention is to provide a coatedmetal substrate particularly useful in the electrorefining of metal.

How these and other objects of this invention are achieved will becomeapparent in the light of the accompanying disclosure. In at least oneembodiment of this invention at least one of the foregoing objects willbe achieved.

In accordance with this invention it has been discovered that a dressingor parting agent composition comprising an aqueous emulsion containingminor amounts by weight of a polar, saturated, substantiallywater-insoluble, aliphatic organic compound and a sulfur-containingmaterial is useful and yields improved results when employed in anoperation for the preparation of metal cathode starting sheets, such ascopper cathode starting sheets. Further, it has been discovered that anelectrically conductive substrate, such as a metal substrate, coatedwith a parting agent in accordance with this invention and comprising anaqueous emulsion containing a polar, saturated, substantiallywater-insoluble, aliphatic, organic compound and a sulfur-containingmaterial, permits the ready separation of electrodeposited metal fromthe coated substrate or surface.

The polar, saurated, substantially water-insoluble, aliphatic, organiccompound which may be of commercial grade or reagent grade qualitycomprising one of the components of the parting agent composition inaccordance with this invention is selected from the group comprisingfatty acids, fatty alcohols and derivatives thereof, such as esters andglycerides. The polar, saturated, organic compound may be liquid orsolid at a temperature in the range from about 60 F. to about 100 F.,more or less. It is required, however, that the polar, saturated,organic compound be substantially water-insoluble at such temperatures.Specifically, the polar, saturated, organic compound should have awater-solubility not in excess of about 5% by weight at about 150 F.based on the resulting solution. The purpose of the polar, saturated,organic compound in the parting agent composition of this invention isto form a film or barrier on the substrate or surface to which it isapplied such that after electrodeposition of metal thereon theelectrodeposited metal can be stripped therefrom with little difficultyand substantially in the shape or outline of the substrate surfaceitself.

Polar, saturated, organic compounds which have been found to be usefulin compositions in accordance with this invention include the fattyacids, such as stearic acid, the fatty alcohols, such as decyl alcohol,lauryl alcohol, tridecyl alcohol, myristyl alcohol, cetyl alcohol, i.e.a C straight chain alcohol, hexadecyl alcohol, i.e. a C branched chainalcohol, stearyl alcohol, arachidyl alcohol, the aliphatic esters, suchas butyl stearate, isopropyl palmitate, isopropyl stearate, glycerolmonostearate, ethylene glycol monostearate, diethylene glycol stearate,propylene glycol stearate, sorbitan monostearate and sorbitantristearate.

Other polar, saturated, aliphatic, organic compounds useful in thepreparation of compositions in accordance with this invention includedecanoic acid, palmitic acid, ntridecanoic acid and their highermolecular weight homologues. Polar, saturated, fatty, substantiallywater-insoluble, aliphatic, organic compounds containing at least carbonatoms per molecule, such as 12-60 carbon atoms per molecule, and havinga solubility in water not greater 4 than about 5% by weight in theresulting solution at a temperature of about F. yield satisfactoryresults. Mixtures of such organic compounds are also usefully employedin the compositions of this invention.

The other component of the dressing or parting agent compositions ofthis invention is a sulfur-containing material. This other component maybe prepared by dissolving sulfur in a polar, saturated, fatty, organiccompound such as the aforementioned polar, saturated, substantiallywater-insoluble, aliphatic, organic compound in compositions of thisinvention. A solution prepared by dissolving sulfur in n-hexadecylalcohol has been found to yield satisfactory results.

Sulfur-containing compounds which have been found to be useful includemercaptopropionic acid, n-butyl-sulfide, n-octyl mercaptan and laurylmercaptan. In general, sulfur-containing organic compounds, such asalkyl sulfides and alkyl mercaptans containing at least four carbonatoms per molecule, such as alkyl sulfides and alkyl mercaptanscontaining from four to twenty-four carbon atoms per molecule, areuseful in the practice of this invention.

The amount of sulfur-containing material in compositions in accordancewith this invention is small, less than about 1% by weight of thecomposition. For example, it has been observed that in the manufactureof copper cathode starting sheets employing a dressing or parting agentcomposition in accordance with this invention if the sulfur-containingmaterial content of the dressing is too high the resultingelectrodeposited copper will be lacy i.e. have the appearance of lace.

Any suitable emulsifying agent may be employed in the preparation ofaqueous emulsions containing the polar, saturated, aliphatic, organiccompound and the sulfurcontaining material in accordance with thisinvention. Satisfactory results have been obtained in the manufacture ofcopper cathode starting sheets when the emulsifying agent employed inthe preparation of the parting agent compositions comprises a sodiumdodecylbenzene sulfonate. Other useful emulsifying agents include linearalkyl aryl sulfonates and the corresponding water-soluble salts andlinear alcohol sulfates and the corresponding watersoluble salts.

In the dressing or parting agent compositions in accordance with thisinvention the polar, saturated, aliphatic, organic compound is usuallypresent in an amount in the range 220% by weight based on the aqueousemulsion and the sulfur-containing material is usually present in theemulsion in an amount in the range 0.05 to 0.15% by weight. Theemulsifying agent is present in an amount effective to emulsify thepolar, saturated, substantially water-insoluble, aliphatic, organiccompound and is usually present in an amount in the range 0.4-4% byweight.

The dressing or parting agent composition may be applied by any suitablemeans to the substrate upon which the metal is to be electrodeposited,such as swabs or rollers, or by spraying or by dipping or immersing thesubstrate, e.g. the copper starting blank, into the emulsion and thenraising the blank and permitting the excess emulsion to drain. Usuallywhen dipping the blank in the emulsion it is not necessary to hold theblank therein for more than one or two seconds. Holding the raisedblank, after dipping, above the dipping tank to drain excess emulsioninto the dipping tank is useful to decrease consumption of the emulsion.

Copper starting blanks coated with a composition in accordance with thisinvention were employed in electrolytic cells under commercial copperrefining conditions for the preparation of copper cathode startingsheets. The resulting electrodeposited copper cathode starting sheetswere smooth and without defect and were readily stripped from the blankswithout diificulty.

The following are descriptions of compositions and methods for thepreparation of compositions in accordance with this invention. Water ata temperature of about -175 F. was introduced to within about 18" fromthe top into a tank measuring 48" high, 48" long and 18" wide. The tankwas also provided with a A horsepower Lightnin mixer which had a shaftabout 3 feet long to which were fixed two propellers, each about 3" indiameter. Seventy pounds hexadecyl alcohol and fourteen pounds Sulframin85 flakes, a sodium n-dodecylbenzene sulfonate were added to the hotwater in the tank. More hot water was then added to within 4" from thetop of the tank, and the resulting admixture was agitated for at leasteight hours by means of the Lightnin mixer. The order and the rate ofaddition of the components are not critical. It is preferable, however,to first add the polar, saturated, aliphatic, organic compound, such asthe fatty alcohol, and then to add the emulsifying a ent.

The following day, when the resulting emulsion had cooled to aboutambient temperature, agitation was again commenced and about 1.4 poundsmercaptopropionic acid was added. Agitation of the admixture wascontinued for at least about 2 hours.

The resulting emulsion now contained hexadecyl alcoholabut 5 by weightSulfrarnin *85-about 1% by weight mercaptopropionic acidabout 0.1% bywelght.

The sulfur-containing material, such as the thiolactic acid, is usuallyadded last since sulfur-containing materials, particularly the organicsulfur-containing compounds, have an unpleasant odor, especially whenwarmed. Cooling of the emulsion before the addition of thesulfur-containing material is a matter of convenience and preference soas to decrease the odor. Upon the addition of the mercaptopropionic acidthe emulsion is ready for use by immersing therein the copper blanks.

After immersion, the copper blanks are placed in commercial copperelectrolytic cells and substantially pure copper electrodepositedthereon. When the desired thickness, about of electrodeposited copperhas been reached, the blanks containing the electrodeposited copper areremoved from the cells and the resulting formed electrodeposited copperstarting sheets are pulled or stripped therefrom as smooth, continuous,coherent, essentially hole-free sheets.

Other aqueous emulsions found to be useful and to yield satisfactoryresults in accordance with the practices of this invention includeaqueous emulsions having the compositions:

In the preparation of aqueous emulsion compositions in accordance withthis invention, as the sulfur-containing material component of theemulsion a sulfur solution prepared by the addition of 4 grams ofelemental sulfur per 1000 cc. of hexadecyl alcohol followed by heatingto a temperature in the range about 180-l90 F. to dissolve the sulfur,thereby yielding a sulfur solution containing 0.4% by weight sulfur, hasbeen found to be useful, particularly in combination with hexadecylalcohol as the polar, saturated, substantially water-insoluble,aliphatic, organic compound.

Other sulfur-containing materials found to be useful include n-laurylmercaptan and n-octyl mercaptan. These may be added directly to theagitated emulsion.

As indicated hereinabove the practice of this invention is not onlyapplicable to the manufacture of copper cathode starting sheets butwould also appear to be applicable to the manufacture of nickel cathodestarting sheets and the like. Also, as indicated herein, the practice ofthis invention is applicable to electroforming operations to improve andaid in the release of the electrodeposited metal from the substratematerial.

As will be apparent to those skilled in the art in the light of theforegoing disclosure, many modifications, alterations and substitutionsare possible in the practice of this invention without departing fromthe spirit or scope thereof.

I claim:

1. A material comprising an electrically conductive substrate coatedwith a film or layer of a composition comprising 220% by weight of apolar, saturated, substantially water-insoluble, aliphatic, organiccompound selected from the group consisting of fatty acids, fattyalcohols and ester and glyceride derivatives thereof and a minor amountin the range 0.054% by weight of a sulfur-containing material.

2. A material in accordance with claim 1 wherein said electricallyconductive substrate is a smooth plate of rolled copper.

3. In an operation wherein a parting agent is applied to an electricallyconductive substrate, the parting agent serving as an aid for thestripping and removal of metal subsequently electrodeposited on saidsubstrate, the improvement which comprises employing as said partingagent a composition comprising an aqueous emulsion containing 2-20% byweight of a polar, saturated, substantially water-insoluble, aliphatic,organic compound selected from the group consisting of fatty acids,fatty alcohols and ester and glyceride derivatives thereof and about0.05-1% by weight of a sulfur-containing material.

4. A method in accordance with claim 3 wherein said electrodepositedmetal is a metal selected from the group consisting of copper, nickeland the like.

5. A method in accordance with claim 3 wherein said electrodepositedmetal is copper.

6. A method in accordance with claim 3 wherein said sulfur-containingmaterial is selected from the group consisting of sulfur solutions,mercaptopropionic acid, nbutyl sulfide, n-octyl mercaptan and laurylmercaptan.

7. A method of making copper cathode starting sheets which comprisesapplying to the surface of a smooth copper plate an aqueous emulsioncomprising a minor amount in the range 220% by weight of a polar,saturated, substantially Water-insoluble, aliphtaic, organic compoundselected from the group consisting of fatty acids, fatty alcohols andester and glyceride derivatives thereof and a minor amount in the rangeof 0.05-1% by weight of a sulfur-containing material and a minor amountof an emulsifying agent for said polar, organic compound,electrodepositing substantially pure copper on the surface of thethus-coated copper plate and stripping the resulting electrodepositedcopper from said copper plate su'bsantially in the form of a smooth,coherent, essentially holefree, copper sheet.

8. A method in accordance with claim 7 wherein said sulfur-containingmaterial is selected from the group consisting of alkyl sulfides andalkyl mercaptans containing from 4 to 24 carbon atoms per molecule.

9. A method in accordance with claim 7 wherein said sulfur-containingmaterial is mercaptopropionic acid.

10. A method in accordance with claim 7 wherein said sulfur-containingmaterial is prepared by the addition of elemental sulfur to hexadecylalcohol in the proportion 7 8 of about 4 grams of elemental sulfur per1000 cc. of FOREIGN PATENTS hexadecyl alcohol.

341,246 1/1931 Great Britain. References Cited OTHER REFERENCES UNITEDSTATES PATENTS 5 JOHN H. MACK, Primary Examlner 2,555,321 6/1951 Dalton204-2 0,046,203 7/1962 Caldwell 204 12 T. TUFARIELLO, Asslstant Exarnmer3,271,190 9/1966 Nadeau 106-2 U.S. C1. X.R. 3,231,339 10/1966 Edgar204-12 10 204-12 630,796 8/1899 Becker 2044 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3,523,873 Da ed August 11, 1970 Inent EUGENE MITCHELL ELKIN It is certified that error appears in theabove-identified patent and that: said Letters Patent are herebycorrected as shown below:

In Column 7, under "References Cited UNITED STATES PATENTS", the secondreference is incorrect. This line should read 3,0 6,203 7/1962 Cadwell20 +--12 slim ocfzv 1970 (SEAL) Attest:

Edward M. Fletcher, 11;

Attcsting ()ffim WHIIIIAH E. JR.

Commissioner of Patents FORM POWSO USCOMM-DC 6OS7B-P6O U s GOVERNHENYPRINTING OFFICE I OS66 334

